In 3GPP (Third Generation Partnership Project), according to a radio communication system corresponding to LTE (Long Term Evolution) having a standard being currently designed, a radio base station eNB performs assignment of a radio resource in radio communication between the radio base station eNB and a radio terminal UE (for example, refer to Non Patent Literature 1). Furthermore, in the radio communication system corresponding to the LTE, one of FDD (Frequency Division Duplex) and TDD (Time Division Duplex) is employed in the radio communication between the radio base station eNB and the radio terminal UE.
Moreover, in an LTE (TDD-LTE) radio communication system employing the TDD, there has been discussed a feature where the radio base station eNB performs control for adaptively directing a beam (adaptive array control) toward the radio terminal UE at the time of transmission of a downlink radio signal, in order to ensure communication quality between a radio base station eNB and a radio terminal UE that is moving.
For example, in the next-generation PHS (XGP) radio communication system, a frequency band for a downlink radio signal assigned to a radio terminal is equal to a frequency band for an uplink radio signal. Thus, a radio base station is able to calculate an antenna weight for the downlink radio signal with the frequency band, which is equal to that of the uplink radio signal, on the basis of a propagation environment of the frequency band for the uplink radio signal, which is understood by the uplink radio signal from the radio terminal.
Meanwhile, in the TDD-LTE radio communication system, OFDMA (Orthogonal Frequency Division Multiplexing Access) is employed in downlink radio communication and SC-FDMA (Single Carrier Frequency Division Multiple Access) is employed in uplink radio communication. In these multiplexing schemes, a radio resource is arranged in two dimensions of a frequency and a time to realize user multiplexing, and there is a case in which a frequency band for a downlink radio signal assigned to a radio terminal UE is not equal to a frequency band for an uplink radio signal.
Therefore, when the uplink radio signal was received from a radio terminal UE, a radio base station eNB may not calculate an antenna weight for the downlink radio signal with the frequency band, which is equal to that of the uplink radio signal, on the basis of the propagation environment of the frequency band for the uplink radio signal.